Small 2 cycle engine runs best on half choke. I've played with dozens of engines, I've cleaned and adjusted many Carbs. This one has me stumped.

Runs with the choke on..!??.... the choke cuts off the air supply or in some cases adds extra fuel.. With respect to both, ..they accomplish one thing.. the richen up the fuel mixture..SO with that..,, your engine is starving for fuel ... Its usually the low speed jets are clogged...there are numerous SMALL air and fuel passages that are sometimes hard to clean properly.. Take the carbs to a qualified professional and let him clean and set them.. (if you removed any of the screws that affect the jetting/air/fuel mixture/idle circuit,, they MUST be set back to the factory settings)..

If the plugs are ok and your engine is not smoking after starting and running ..Sounds like either of three things..all with the carburetor .First the carb has a adjustment screw for air/gas mixture on the side if the carb where it attaches to the engine..try this start the engine and at about half throttle..now adjust the screw clockwise until the engine starts to miss and bogg down then back the other way until it starts missing and bogging again. Then slowly adjust back and forth until you hear the engine run the smoothest..give it more throttle if it starts to run rough do the same procedure until you get the results you want..if it is the mixture problem this will take care of it..if this doesn't it it may be your fuel jet in the bowl dirty or the blow float sticking..if you are not familiar with carbs best to have a professional look at it..you can drop the bowl by removing the bottom bowl and clean it out...check to see if the float easly moves up and down..replace the bowl and go from there..worse scenario new or rebuilt carb...good luck..

yes as well as the carbs are still dirty

This is a tell tale sign of a lean fuel mixture. By choking the unit you are manually creating a richer fuel mixture. I would purchase a compression tester from a local parts store and check compression. If that's ok, I'm willing to bet the problem is still carb related. Two stroke carbs are tricky to clean because of high/low ports that are one way and sometimes impossible to clean. Did you remove high and low needles when cleaning carb? Another trick is to mix seafoam with your gas, then mix two cycle oil to proper ratio. Use 2 ounces seafoam to one gallon of gas, then mix two cycle oil to proper mix. Hope this helps! Good luck and happy wrenching!

I’m happy to assist further over the phone at https://www.6ya.com/expert/layne_0fccff498c319c32

1 and 2 run off different coils so its not electrical
do a compression test after checking all valve clearances
clean the carbs
check for any cracked hoses to the fuel tap,
and check for fuel tap operation, and its not running on prime, no fuel should flow in the run or reserve position until the engine is running.

the ajustment need to be set where they were originaly, needle position and mixture screw. the carbs are not suppling enofe fuel, was there any torn seals or diaphrams.

your engine will **** in an average of almost a teaspoon of dust an hour of running without a airfilter on. this dust wears out the rings in your engine and everything else it touches in your engine. Lower compression and partially clogged jets lower the vaccum that your carbs pull in. Your bike should have a vaccum operated petcock that allows the fuel into your carbs. My guess is that you have low vaccum pressure. You might just need to replace a vaccum line or a petcock. Try pulling off the vaccum line from the front of the second carb and sucking on it until you see the fuel line fill up a little (don't worry, gas doesn't go threw the vaccum line so you won't get a mouth full of gas). Once you see the line about half full of gas or better. Try starting it up without the choke (engine should already be warm). The reason why I think this might be the problem is because when you choke a engine on these carbs, you increase the vaccum in the lines. Let me know if when it is warm, before you start it, if it already has about half of the gas line filled up. Good luck and let me know how it works out.

look on the side of the carb for 2 small adjusting screws they will be almost touching( they will have springs on the threaded part of the scews) the heads will be small 3/16 " open these counterclockwise, this allows more fuel in. The one closest to the engine is for the idle mixture the other is for high speed , tilling speed. 1/2 to 1 turn may help, good luck . try PER small engine tecnical forum online

That's a good indication the air/fuel mixture is off. Before you try to adjust the carb, make sure the air filter and prefilter are clean. If they are filthy, replace them. Make sure the carb looks clean when you take the air filter off.

Adjustments to the carb are not easy and if you don't have a service manual or operators manual it's probably something you don't want to tackle, unless you have a good working knowledge of small engine carbs.

I would probably have that serviced. But first, I couldn't resist taking the air cleaner off, turning the throttle up about half way, and squirting a small amount of starter fluid into the carb, then crank it to see if it starts.

Do not choke it. If it starts, run it a while, but put a clean air filter and prefilter on it while it is running. Then see how it runs, and if it seems okay, try cutting a little with it.

Have you checked the plug(s) lately? Sometimes lots of things combined will cause one small problem. I didn't mean to write a book here. If you do all these things and it runs okay now, and after you finish you change plug(s), and when it gets cold again (next day) try and start it again with the choke. Make sure the throttle is moved up about 2/3 of the way.

If you run into the same backfiring problem, it's time to take it in to see the doc. Probably air/fuel misture is off, and that's why it backfires when you choke it. Good luck!

Sirwriter

when you get the bike started you need to adjust the pilot air screw. here's how= turn in clock wise until engine falters(mark that spot with a pin)then out counterclock wise until the engine falters(mark that spot also) then put the screw in half amount adjustment of the two marks.that will take care of if it is to lean or to rich.make sure the engine is good and warm before doing so.